Computer systems, particularly personal computer systems (PCs), use peripheral devices for data storage and retrieval and communications among other tasks. Peripheral devices include hard drives, floppy drives, Compact disk (CD) devices which include Compact Disk Recordable (CD-R) drives and Compact Disk Re-Writeable (CD-RW) drives, tape drives, modems, keyboards, pointing devices (mouse), and scanners. Peripheral devices may be mounted internally, that is, inside the computer case, or mounted external to the computer case. Peripheral devices are connected to, and communicate with, the computer through an interface, such as an Integrated Drive Electronic (IDE), Enhanced Integrated Drive Electronic (EIDE), AT Attachment Packet Interface (ATAPI), Small Computer System Interface (SCSI), or Peripheral Component Interconnect (PCI) interfaces.
User installed peripheral devices that are internally mounted are generally not desirable. Users typically lack the necessary skills for such installation and configuration. Installation involves opening a computer case, securing the device to the case, connecting power lines to the power supply, connecting data lines to the motherboard, installing a controller card on the motherboard, and configuring jumper blocks on the device (such as master/slave on IDE, SCSI ID""s for SCSI). After installation, the user must then configure the device for operation in the system. This may involve resetting parameters in the Basic Input Output System (BIOS) and/or configuring files in the operating system (OS). Although the plug and play mechanism has simplified the configuration aspects somewhat, installation is still beyond most users.
One solution to this problem is to have peripheral devices externally coupled to preconfigured and pre-installed ports, such as serial ports or parallel ports. These types of ports are standard on most computers. The user would merely connect a cable from the device to the appropriate port on the computer case, and connect a power supply cable to a wall socket. A problem which may arise, however, is that serial ports are generally slow. Further, some serial port controllers lack data buffering, which may cause data to be lost when higher communication speeds are employed. Moreover, external peripheral devices are also frequently used with portable computers, such as laptops, which have few, if any, internal device bays. Problems may also arise when using the parallel port. The parallel port is not a system bus, but rather is a connecter to a card that is connected to the system bus. The parallel port is designed to send and receive several data bits simultaneously on multiple wires. The card which is connected to the system bus, with a parallel chip set, converts the parallel data into system bus data, and vice versa. Generally, different parallel chip sets are used among different computer systems. Consequently, many incompatibilities may arise when external devices employing a single communication standard are used with different parallel port chip sets, possibly employing different and incompatible standards. Moreover, the parallel port may operate in a variety of modes, such as bi-directional, ECP (Extended Capability Port), SPP (standard printer port), and EPP (enhanced parallel port) modes. In some computers, certain modes are too slow to support high data rate devices such as a CD-RW, and thus the device cannot operate in that mode. To ensure proper operation, a user would have to alter the parallel port settings in the BIOS.
Another solution is to add an interface card to the system, such as a SCSI card. This would allow a user to plug the external device into the card. However, this solution requires installation of the card, typically into an ISA or PCI expansion slot on motherboard, which is internal to the computer case as described above. Installation of an interface card also generally incurs the difficulties associated with user configuration of devices installed internally to the computer system.
Yet another approach involves using the universal serial bus or USB. This bus features an external connection point, and thus would allow for a simple hook up of the external device. The USB is featured on most computers built after 1997. The USB operates with Windows 98 and Windows 2000, and thus has support in those operating systems. However, use of the USB presents problems for certain applications. One problem is that the USB is a shared bus enabling multiple devices to be plugged into the same bus at the same time, and thus all sharing the finite total bandwidth of the bus. The bandwidth availability for any one of the multiple devices may therefore be limited.
A further problem is presented by the available modes of data transfer on the USB. Currently, there are generally two communication modes for transferring data, a bulk mode and an isochronous transfer mode. The bulk mode provides error correction thereby generally ensuring that if erroneous data is included within a data packet, the packet will generally be resent until it is delivered in proper form. While such error correction and retransmission helps ensure accurate data transmission, the processes of correction and retransmission may substantially slow down the communication rate for bulk mode communication. Further, while isochronous data transmission is transmitted first and provided with pre-allocated bandwidth on the USB, bulk mode is generally assigned a low priority for transmission and is thereby not provided with a guaranteed bandwidth. Bulk data is generally transmitted only after higher priority data has been transmitted first.
Thus, while the integrity of bulk data can be ensured, data transfer is frequently interrupted by higher priority data. Therefore, this mode is not suited for use with devices that require a continuous flow of data such as CD-R or CD-RW devices. Note that when writing to a CD-RW device or other xe2x80x9ccontinuous flowxe2x80x9d data receiving devices such as a CD-R, or digital audio tape device, the data flow should preferably be uninterrupted . If there is a break in a bulk data transmission which is later resumed, the CD-RW, or other data receiving device, may not be able to seamlessly resume operation where a prior transmission ended. In an application such as writing to a CD-R disc, this may cause a CD xe2x80x9cburnxe2x80x9d to fail.
These problems originate with the design of the USB. The USB is designed for HID (Human Interface Device) devices, e.g. keyboards, mice, joysticks, etc. These devices have low data rate speeds and generally do not receive continuous streams of data. Consequently, there is generally little native support in computer operating systems for high speed, constant flow devices such as CD or CD-RW drives.
Therefore, there is a need in the art for an external interface for a computer that has a high data rate and which is compatible with the operating system in use.
These and other objects, features and technical advantages are achieved by a system and method which includes enabling an external device to be connected to an interface on a host computer which is well supported by the native operating system of the host computer and has a high, guaranteed communication bandwidth, and incorporating error correction information directly into a data stream between the host computer and the device as such data is sent. Introduction of the error correction information into the data stream may be accomplished employing hardware, firmware, software, or a combination of two or more of the three approaches. Such error correction information may be introduced by either the host computer or the external device. A data reliability mechanism may implement data retransmission according to established protocols such as TCP, Kermit, or Zmodem, or may implement error correction according to the Reed-Solomon algorithm. The listed data retransmission and error correction code protocols are well known in the art and will therefore not be discussed in detail herein.
In a preferred embodiment, the Universal Serial Bus (USB) on a host computer is employed for communication with the external device. The USB is generally well supported on personal computers and generally has a high communication bandwidth. Preferably, the Isochronous Transfer Mode is employed for data transmission between the USB and the external device, thereby enabling a high pre-allocated bandwidth to be reserved for the external device whose data reception demands are latency-intolerant.
Herein, data used for error correction purposes is referred to as xe2x80x9cerror correction dataxe2x80x9d or xe2x80x9cerror correction code,xe2x80x9d and data intended for delivery to, and use by, the external device is referred to as xe2x80x9cdevice dataxe2x80x9d or xe2x80x9creal dataxe2x80x9d. A general term for a mechanism for ensuring accurate data delivery is xe2x80x9cdata reliability mechanismxe2x80x9d. Preferably, the data reliability mechanism employs error correction data to determine whether data in a packet or other data container is faulty. Upon determination that faulty data is present, the data reliability mechanism may either correct the data at the device which received the faulty data, without retransmission, or request a retransmission of the data from the transmitting device. Correction of data at a receiving device (as opposed to retransmission of the packet concerned) is referred to herein as xe2x80x9con-sitexe2x80x9d data correction. Preferably, both the host computer and the various possible external devices may be transmitters and recipients of data, and both may implement data reliability mechanisms. Herein, a xe2x80x9clatency-intolerantxe2x80x9d operation or device refers to a condition wherein a delay in data transmission substantially impairs a process or the operation of a device and where such impairment is not necessarily cured by supplying the required data at a later time.
In a preferred embodiment, error correction data is preferably introduced into the data stream as the data leaves the host computer for the connected external device. The error correction data may also be introduced into a data stream as such a data stream leaves the external device bound for the host computer. Preferably, both the host computer and external device have the ability to process the error correction data received along with the device data to determine whether a transmitted data packet contains corrupted data. Depending upon the nature of the error correction scheme or data reliability mechanism employed, a response to a determination that transmitted data contains errors may include having the receiving device (whether host computer or external device) request that the data packet containing the erroneous data be retransmitted. Alternatively, the data receiving device may correct the erroneous data upon receiving the data where the error correction scheme provides sufficient information for such correction.
It is an advantage of the present invention that an external interface is provided which has a high data rate and is well supported by the operating system native to a host computer.
It is a further advantage of the present invention that sufficient bandwidth may be pre-allocated for communication with an external device employing the high data rate external interface.
It is a still further advantage of the present invention that error correction may be implemented for high data rate communication on the external interface.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.